Patent GB-772178-A (GB)
Title: Production of tris(n-dimethyl) phosphoric acid amide
Inventor: ISHAM ROBERT M
IPC: C07F9/22
Filed: 1953-12-10
Abstract: Tris-(N-dimethyl) phosphoric acid amide is obtained by reacting dimethylamine with a phosphorus oxyhalide in the presence of an inert, substantially non-hydroscopic, slightly hydrophylic diluent comprising a non-cyclic ether which is a solvent for the said reactant and for the tris-(N-dimethyl) phosphoric acid amide and which wets but does not dissolve the dimethyl amine hydrohalide formed, and which boils within the approximate range of 100 DEG  to 390 DEG  F., controlling the reaction conditions to effect the formation of tris-(N-dimethyl) phosphoric acid amide and dimethyl amine hydrohalide and separating and recovering the reaction products.  It is preferred to use phosphorus oxychloride as the oxyhalide reactant but other oxyhalides specified are phosphorus oxybromide, oxybromodichloride and oxychlorodibromide. The amine hydrochloride, being a crystalline solid, may be separated from the reaction mixture by decantation, filtration or centrifugation and the separated hydrochloride may then be treated with aqueous alkali, e.g. by heating with an aqueous solution of caustic soda to regenerate the amine which may then be recycled to the reaction zone in admixture with a fresh charge of the dimethylamine.  The dimethylamine is preferably employed in slight stoichiometric excess, the optimum molar ratio of phosphorus oxychloride to dimethylamine being from 1 : 6.2 to 1 : 8.  Any excess amine may be recovered and recycled.  The reaction temperature should be maintained within the range of 32 DEG F. to 240 DEG  F. and sufficient time must be allowed for the phosphorus oxychloride to react completely, a reaction period of about 2 hours at 200 DEG  F. being generally suitable.  It is preferred to carry out the reaction by adding the oxychloride solution to the amine solution.  Instead of separating the amine hydrohalide and then decomposing the latter to regenerate the amine, the initial reaction product may be treated with a controlled amount of caustic soda solution to decompose the amine hydrochloride in the mixture and by employing a refrigerated reflux the liberated amine together with any excess unreacted amine may be recovered.  The mixture may then be heated to a high temperature to remove all the water by azeotropic distillation, the diluent being freed of water and returned to the still.  The diluent may then be distilled off to leave a residue which may be distilled under reduced pressure in a smaller still to recover the tris-(dimethyl) phosphoric amide as distillate.  In order to obtain high yields of product the dimethylamine used should be substantially free of monomethylamine. The dimethylamine may, however, be used in admixture with triethylamine since the latter has no appreciable effect on product yield.  The trimethylamine does not take part in the reaction and can therefore be recovered from the product by distillation.  This variation may be used to separate triethylamine from a mixture thereof with diethylamine.  In one form of this process a mixture containing water, mono-, di- and trimethyl amine obtained by the reaction of ammonia with methyl alcohol is fractionated to recover a mixture of the amines which is then further fractionated to separate the monomethyl amine and yield a fraction comprising a mixture of di- and tri-ethylamines which may either be used as such in the oxyhalide reaction although preferably the mixed amine fraction is subjected to further fractionation to yield a dimethyl amine-trimethyl amine azeotrope as overhead and pure triethylamine as bottom product and the overhead fraction is submitted to the phosphorus oxychloride reaction to form the tris-(N-dimethyl) phosphoric acid amide and dimethylamine hydrochloride.  If any unreacted dimethylamine remains the reaction mixture may be treated to recover a mixture of trimethylamine and the unreacted dimethylamine which may be fractionated to yield an azeotropic mixture of dimethyl- and trimethyl-amines which may be recycled to the reactor and a fraction consisting of substantially pure trimethyl amine.  When sufficient phosphorus oxychloride is employed to react with all the dimethylamine present, the diluent solution is separated from the dimethylamine hydrochloride and then subjected to distillation, e.g. at atmospheric pressure and with the use of refrigerated reflux, to recover substantially pure trimethylamine. An example is given in which dibutyl ether is used as the non-cyclic ether diluent for the production of the tris-(N-dimethyl) phosphoric acid amide from dimethyl amine and phosphorus oxychloride.  A comparative example is also given to show that di-isopropyl ether is unsatisfactory for use as the diluent and it is stated that toluene, n-heptane, 2,2,4-trimethyl pentane, dioxane and the diethyl ether of ethylene glycol are also unsatisfactory when used as diluents.  Specification 675,294 is referred to.